Potassium (K) deficiency causes changes in vascular resistance and alters plasma renin activity. In this proposal we plan to document the changes in systemic and renal hemodynamics and in plasma renin activity that are caused by a K deficient diet in rats. Studies will be performed in K deficient conscious intact rats as well as in the isolated perfused kidney of the K deficient animals. Renal blood flow will be measured utilizing radioactive microspheres in conscious animals while perfusion flow rate will be measured directly in the isolated perfused kidney. The role of K per se, prostaglandins and angiotensin in the maintenance of the systemic and renal circulation will be assessed using various angiotensin antagonists and prostaglandin synthesis inhibitors. The mechanism of hyperreninemia will be assessed in the isolated perfused kidney by altering perfusion pressure, prostaglandin synthesis and K concentration in the perfusate. The exogenous angiotensin II pressor responsiveness of the K deficient rat will be assessed and the role of K, angiotensin II and prostaglandin in altering the responsiveness will be evaluated in the intact rat as well as in the isolated perfused kidney.